Lenore Katz shed 137 pounds, gradually dropping from 272 pounds to 135 pounds, over several years. The 60-year-old grandmother from of Brooklyn, N.Y, has kept the weight off for five years, but she still has moments of panic about falling back into old habits of overeating.

Rates of women who are opting for preventive mastectomies, such as Angeline Jolie, have increased by an estimated 50 percent in recent years, experts say. But many doctors are puzzled because the operation doesn't carry a 100 percent guarantee, it's major surgery -- and women have other options, from a once-a-day pill to careful monitoring.

From NBC’s “The Biggest Loser” to
TODAY’s “Joy Fit Club”
and Jenny Craig commercials, there’s no shortage of promotions for people who have transformed themselves by losing 100-plus pounds through diet and exercise programs. “
I am a whole new woman
," Ali Vincent, who lost 112 pounds and this week became first female winner of the hit show “Loser,” told TODAY.

But what happens after the fat pants are gone?

Some are surprised to discover the struggle doesn't end when they hit their goal weight. While the outside world sees a slimmer body, their personal body image often remains distorted. Katz remembers the pain of standing out in a crowd as “the fat one.” As a result, she regularly feels the nagging worry of “Will I gain it back?”

For all the celebration over people who lose massive amounts of weight, diets usually fail in the long run, studies show. A recent weight-loss maintenance study from Duke University found that after losing an average of 18.7 pounds over six months of diet and exercise, most dieters regained an average of nine pounds over the next 2 ½ years. Up to two-thirds of dieters gain back most of the weight they lost, according to an analysis of 31 diet studies released by researchers at the University of California, Los Angeles last year.

What dieters often don’t realize is, while they can relax a little about how much they eat, they have to remain vigilant. The worst mistake dieters who have lost a lot of weight make is to think that they're "done," and that they no longer have to choose their food wisely and responsibly.

It's not over yetIn my practice, I have consulted with hundreds of men and women lost weight on various diets and then gained it back. It seemed like these dieters were willing to put up with almost any restriction, as long as they knew that, at some point, the punishing diet plan would be over. But to maintain your weight loss, you always have to pay attention to what you eat. Yes, always, no matter what you weigh.

“People need to think of [obesity] as a chronic disease like hypertension and diabetes,” says obesity expert Dr. Lawrence Appel, professor of medicine at Welch Center for Prevention, Epidemiology and Clinical Research at the Johns Hopkins School of Medicine in Baltimore. “It’s a lifelong issue.”

My client Katz says her strongest defense against regaining the weight is regular internal conversations with herself. When she’s in a tempting food situation, for example, she’ll say, “I am in charge, not the food. What I eat in private, I wear in public.”

Whether you’ve lost 10 pounds or 100 pounds, there’s a greater chance of keeping it off if you incorporate better habits into your lifestyle, instead of radically changing it as many diet plans promote.

Here are some basic tips to help you do that:

Allow yourself a weight-gain range of 3-5 pounds without panicking. When you’re at the lower end of your range, give yourself a little freedom to enjoy some of your favorite foods. If your weight goes up another pound or two, then you’ll need to pull in the reins again to keep yourself within your desired range.

Find a consistent tool to help you stay in touch with your body weight. You can weigh yourself on a scale daily or one or two days a week. I prefer weighing Fridays and Mondays — a way to
control weekend splurges
when overeating is most common. Or you can use an article of clothing, such as a pair of your favorite skinny pants, that will become your frame of reference. Try them on the last day of each month. Clothing doesn’t lie (and don’t try to blame the dry cleaner for shrinkage!).

Get rid of “fat” clothes that are too big on you and no longer fit. Why would you ever want to fit into that size again? Dress the body you have.

Bonnie Taub-Dix is a registered dietitian in New York City and a spokesperson for the American Dietetic Association.